Cobra 138XLR Cb radio. A few restoration tips.

[@Wheelabarraback]

Thanks for posting and getting me interested in repairing my Cobra to get it back on the air again . 👍

[@rodneystuder]

Mike I've been watching your videos for a while now. I just wanted to drop you a note and tell you how thankful I am to have someone like you that isn't stingy and doesn't mind sharing his knowledge with those that aren't as knowledgeable about radios. I will be restoring a cobra 139xlr. I've ordered the tantalum and will get the electrolytic caps as well. There's some scratch in the knobs other than that it seems fine and works as it should super clean with no hack mods. Again this is just a thank you comment have a great one and please continue what your doing

[@Z4NL]

Thanks for this video. Our club recently got a 138XLR donated. Had been in storage since 1977, including all documentation, invoice, mic in original packing. Very neat but test showed no TX or RX. Replaced all the caps in the area of the 858 and replaced defective (hard to find) hybrid VCO chip UHIC-005. Works like a charm again. If any of you needs a new UHIC-005 or UPD858 PLL drop me a line. Have several of those in stock.

[@86jekstrom]

What are you asking for one of each?

[@lesjones7019]

Send him one to fix my 138 xlr.

[@Z4NL]

@@lesjones7019 Hi Les, do you still need this chip?

[@peterfong2241]

Blessed love to all, can I get one to buy please an thanks bro, I would love if you could find a nice cobra 138 XLR, an a HR2510 for me too, they don't sell those stuff down here in Jamaica west Indies !!

[@johncunningham5435]

Nice radio; excellent cosmetic condition, these were one of my favorite radio's to work on, "what a classic". Great presentation and tips, "well done Mike".

[@TheRadioShop]

Great tips Mike. I seen so many where they replaced the tants with AE caps. Shows how many non experienced folks are out there.

[@TheDefpom]

The Radio Shop - I have to admit I have done it if I haven't had the right value /package type tantalum in stock, usually I haven't observed any issues from doing it, but as Mike said, some circuit areas the characteristics are critical and only tantalum can be used.

[@lesjones5684]

Why is the modulation so good on my 138 xlr So good 😅

[@TheDefpom]

I agree, I have seen that glue shorting out the voltage regulators on the MPU PCB of the HR2510/Lincoln radios, because the tab is glued to the PCB on top of traces, whenever I get one of those in I pick all that glue off and replace it.

[@mikesradiorepair]

TheDefpom Often wondered how much the parts companies pay the glue company to make that blasted stuff. Someone has to be getting a kickback payment for the damage caused. ;-) That stuff is known for eating the pins off the VCO block and left rear pins on the PLL chip in 2000GTL/148GTL and similar chassis radios. Horrible stuff.

[@lesjones7019]

@@mikesradiorepair I have a 138 xlr virgen. No glue. You can buy it.

[@lesjones5684]

You can fix mine 😂😂😂

[@josephriffle124]

Thank you for responding so quickly. This an eBay radio. When it first came to the bench I looked it over for mods and removed the channel mod from the NB switch. Upon injecting the signal by the book, I was able to bring the rx sensitivity up quite a bit. Been all through the AGC circuit and tracking the voltages, seem to be fine. It haunts me that if one of the IF cans are bad, that I'll never be able to find a replacement. I wouldn't be opposed to replacing all of them if I could find a "kit". I've replaced the electrolytics throughout the receiver section that "may" cause any problems with no luck. Am I right in thinking that if one of the IF cans was bad, that it won't tune? All of the tuning of the cans, I was able to find the "peak" or "sweet-spot" of each. Cobra recommends TR5 upgrade per #1210a bulletin,... waiting on part. Cans available? BTW this radio is super on TX on both AM and SSB

[@NCICRESQ]

I still have my 2nd 138 xlr. It works gr8. But my 1st radio was modified in that the modulation was opened not limited. And I added another 40+ channels including upper & lower SSB. Just by adding a switch and a resistor and diode. I’d love to find someone to do it again.

[@lesjones7019]

I purchased a 980 ssb .very light Compared to the 138 xlr .

[@DonDegidio]

Mike, Nice video. Don't you wish radios like that would come across your bench more often. :-)

[@mikesradiorepair]

Donald D'Egidio Yeah I can dream can't I. :)

[@garyp5522]

As usual Great Vidio. Great radios as is the TRC-449 same radios. I own a couple of each my radios are not as nice as yours though. Mighty clean radio. I assume bubble wrap bag and back on the shelf.

[@mikesradiorepair]

Gary P A customers radio and he said it was going in a vehicle to be used like it should be. No shelf queen here. :-)

[@lesjones7019]

I need my 138 xlr fixed. No transmit Clean like that radio.

[@williamcolvin3609]

The President Zachary T. has a PC-198 Board with the uPD858 chip,but it has no metal box around the PLL chip. Since it is a Uniden 858 board does it require the same updates as the Cobra 138XLR? Since you are an Authorized Repair Technician for President Radios - Do you have any changes that need to be done to the President Zachary T. radio, before I order replacement parts for it? My radio keys up 3 watts and swings to 8 watts on my Dosy 4001 Watt Meter,but when I transmit no-one can hear my radio.

[@lt1caprice57l]

Have a 138XLR. 7003 production number. Noise blanker essentially doesn't work. There *might* be a tiny bit of attenuation, but I think it might be in my head. Could bad capacitors cause that, or would it be something more serious? Someone already tried to adjust it with no success, could barely get a reading on the VM, and adjustment made basically no difference.

[@shartne]

I have several 138 XLR radios. One of the 138s dont have that 2.2uf Tantalum Capacitor? It transmits and receives well. Should I put one there? What will happen when I do? It seems it never had one but maybe someone removed it before I bought it. I replaced every cap exception of that one 2.2 tantalum cap between the test prongs and I wondered should I put one there? I cleaned all the glue I could find. Its under every pancake ceramic cap on the bottom side of the board. And under every large cap too. I would love replace some of those ceramic bypass caps that ground to the chassis. But I have no idea where they sell those big flat ones that go in the radios. I love these radios they sound so good. Different 138 radio that I have that is equally the nice condition as that the one your working on is in, but someone hacked it at the pll they sawed the board with Dremal and I reconnected the traces and it has static or white noise but dont transmit or received. Sad I replaced all caps but it wont work good when it transmits its distorted and their is a bunch squeal like a bypass cap is bad or it off channel or something I think it has had someone turning all the tunning cans but I dont know. I cannot align one yet I dont have the shop manual either to this radio yet. I am looking to buy one if I find one.

[@mikesradiorepair]

Yes, the tantalum capacitor should definitely be in there. For the user there would be no noticeable difference but look at it on a SA and you would see the difference. Why would you want to change the ceramic capacitors? It's rare, extremely rare for a ceramic capacitor to go bad. They are one of the most reliable components in anything electronic. The only exception would be one across the mains input on a AC powered electronic device. They get pounded 24/7/365 because they are attached to AC mains even when a unit is turned off in most cases.

[@shartne]

Thanks for the answer I will put 2.2 uf tantalum in there. On the ceramic capacitor thoughts of replacing them I have another or different 138 that has real problems it is distorted when transmitting and it has a whine or squeal I guess its a capacitor but I changed out all the Aluminum Radial Electrolytic Capacitors so all that is left is the poly and the ceramic. So from what you said its not the ceramic capacitors. I will start changing out the poly caps. I will have to order some LOL. I never have done that before only one time when I broke one cleaning it. Will the PLL make it squeal or whine? or just not. Maybe it is the alignment it may be off channel. I wonder did someone crank up all the cans so now its off channel and all messed up. It was definitely molested. They always remove the slug from the FM Trap that infuriates me and I dont have any extras I have already used them all from people throwing them out. I cannot adjust that FM trap but I can at least put the slug back in it so maybe its not transmitting on all forty channels I just guess how to adjust from look at another radio how far to screw it in. But I dont have a slug and dont know where to buy one? A spectrum analyzer is very costly. What does SA stand for what kind of a meter is that?

[@mikesradiorepair]

Poly caps are also very reliable with the exception of Silk brand that the coating flakes off of. Randomly replacing parts is not the correct way to diagnose a problem. There is no "FM trap" in a CB radio. FM is a modulation type. I think you mean 54MHz trap circuit. SA stands for spectrum analyzer.

[@shartne]

OK thanks for the reply. I guess its just out of adjustment then.

[@mikesradiorepair]

Doubtful alignment is going to do anything for a squeal problem. It has a problem that needs to be diagnosed.

[@Chuck-U-Farlie]

what a coincidence! I happen to have a minty 138XLR with no sonybond in it either. Also a Taiwan 148GTL with no glue. About an hour ago a president washington appeared on ebay for 50 dollars BIN. it was labeled as "for parts not working" but came in the original box, original packing, and untouched accessories. This radio looks brand new! the reason they said it didn't work was that it didn't appear to transmit on SSB. my guess is that they were expecting a carrier and didn't bother to talk into the mic. apparently it was NOS from a family owned CB shop in NY. i sure hope there isn't much glue on it! QUESTION! what do you set the final bias to on 858 SSB radios? 70mA or 15mA? i think this would be a great subject for a video! as always, thanks for all your great vids. i always learn something new here. Merry Christmas!

[@mikesradiorepair]

loosecannonradios 15mA is the correct final bias. This was covered in one of the service bulletins, #1208. You can download it here. www.cbtricks.com/radios/cobra/138xlr/graphics/cobra_138xlr_139xlr_tb1208a.pdf It is very important to make sure this bulletin is done or premature final transistor failure will happen.

[@Chuck-U-Farlie]

thanks Mike. i remember the tech updates, and i guess i have always wondered whether or not 15mA was the optimum bias, or just unidens way of throttling things back to a guaranteed safe zone. I guess i will have to tune it with a scope when my washington gets here and see where things end up.

[@mikesradiorepair]

loosecannonradios On a scope you won't see much other than a slight increase or decrease in output power. What you would want to view if your not using a ammeter to set it would be the spectrum analyzer. I have done it this way and what you want to watch is the second harmonic frequency. Some chassis when the bias was adjusted for minimum 54MHz signal had a current draw extremely close to the factory spec for bias current. Others had no noticeable difference in the second harmonic frequency. Really depends on the driver and final circuit and how there set up.

[@Chuck-U-Farlie]

wow thanks for the advice. i am still in the dreaming stages of having a spectrum analyzer. thought i found one locally, but it was DOA.

[@lesjones7019]

@@mikesradiorepair scope her out. Lol

[@FarpointFarms]

I just picked up a 135 XLR that has an issue that has me stumped. Trans and receive work great in USB and LSB. However on regular AM it receives fine, but has a loud buzz and hardly any audio on transmit. Any ideas?

[@shartne]

I have that problem too on a 138 xlr but I have changed all the electrolytic capacitors. Capacitors are the problem 99 percent of the time in an old radio.

[@knowles217]

I still have all my old radio got uniden madison a cobra 2000 gtl I a 148 gtl dx a midland 13-882c now my 980ssb

[@lesjones5684]

My 138 xlr doesn’t have any glue eather 😅

[@peterfong2241]

Honestly, this circuit board look like the one in the Realistic TRC 480, can someone correct me if am wrong, I would love to fine one of these radio to buy, Watching from Jamaica west Indies !!

[@mikesradiorepair]

Yes, they were all made by Uniden.

[@lesjones5684]

My 138 xlr doesn’t have any glue 😢

[@Ben_3113]

Thanks for your video's. I've just bought myself a Uniden PC122XL, the chrome has the haze you describe. How would you recommend I restore it? It has no dents or scratches, just the haze so I'm hesitant to use any abrasive material which some people recommend.

[@buckaroobonsi555]

What about OS-Con solid caps can those be used in place of tantalum or maybe a film cap?

[@shartne]

He said no dont do that, you have to use a tantalum where the factory puts them there.

[@DAVIDGREGORYKERR]

I cannot see why they cannot run the VCO at 108 and take the unused output from the Johnson counter to feed 26-28mhz back to the PLL input you might be wondering why I am talking about Johnson counter because it is to facilitate direct SSB modulation demodulation on LSB/USB.

[@lesjones7019]

Is the 138 xlr rare. I can't find another one.

[@898doffo]

Good video. What tantalum rating do you recommend to get to replace? I want to do this to my TRC 449 radios and 139 XLR radios.

[@mikesradiorepair]

898doffo I use 50 volt tantalum caps.

[@898doffo]

MikesRadioRepair Thanks for replying. It will be next on the list. :) right now this cobra 142 gtl had a carrier, but no modulation on CB or PA. tried different mics and still nothing. least it has a goood carrier on AM.

[@898doffo]

I wanted to report back. I did both my Realistic 449 and my 139 XLR. :) Radios did work after installing the Vishay 50v 2.2uf tantalum capacitors. Just good to finally do it and have a peace of mind. Thanks again!

[@898doffo]

Back once again to say I did a recap on an old President Washington base radio. I thought I had an extra Vishay tantalum cap laying around, but I was wrong. Need to order or some more lol. Hope you are doing well.@@mikesradiorepair

[@kimberlysmoke9285]

How long a wait to have a 138 xlr restored?

[@FernandoGiannetti-bv8of]

Hola de consige el transistor 2sc1307??

[@hugomartel8552]

Are They any of those on cobra 29?? I have one that doesnt transmit well Also have a cobra 25 with only 2watt of output power (from an astatic meter and internal meter

[@shartne]

have you changed all the electrolytic capacitors? The aluminum ones? The very first thing to do is to recap. Cobra 29s don't have a tantalum cap between the test prongs. This old 138 is completely different from the 29 nothing is the same at all. Well from time to on rare occasion their are maybe one tantalum cap in a 29 but i guess someone may have put it there in place of the aluminum caps. I usually dont see them if I do I leave them in a 29s tantalums last forever. well a very long time its heck of a lot longer then electrolytic aluminum caps do. I do sometimes see a few in 25s and I just leave them there they are almost always fine in a 25.

[@zipper8089]

I have one of these, when I try to transmit, on am, ,the needle stays near 2 watts, on ssb, there is no movement to mention.Is this due to a bad final? It receives ok

[@josephriffle124]

I seem to be having a great deal of problem getting the receive sensitivity below 3 uV for 12 db sinad, though the signal seems to be amplified through the stages. Do you think this glue could be causing the problem? By the way, it's on a 139 XLR , which is the same PCB.

[@mikesradiorepair]

Joseph Riffle Could be any number of things. Not really much glue to speak of in the RX circuits in the 858 chassis but anything is possible. Is the reduced sensitivity in both AM and SSB? If so that eliminates early stages if the receiver and will be after the signal branches off. Could be a bad filter, bad IF transformer can (usually a bad capacitor inside them actually), AGC circuit fault, etc...

[@josephriffle124]

Thank you for responding so quickly. This an eBay radio. When it first came to the bench I looked it over for mods and removed the channel mod from the NB switch. Upon injecting the signal by the book, I was able to bring the rx sensitivity up quite a bit. Been all through the AGC circuit and tracking the voltages, seem to be fine. It haunts me that if one of the IF cans are bad, that I'll never be able to find a replacement. I wouldn't be opposed to replacing all of them if I could find a "kit". I've replaced the electrolytics throughout the receiver section that "may" cause any problems with no luck. Am I right in thinking that if one of the IF cans was bad, that it won't tune? All of the tuning of the cans, I was able to find the "peak" or "sweet-spot" of each. Cobra recommends TR5 upgrade per #1210a bulletin,... waiting on part. Cans available? BTW this radio is super on TX on both AM and SSB

[@stuartclark5191]

Do you know anything about super jopix 2000 ,signal meter hardly moves no one hears me at all.

[@Stover159]

I just got a 138 off eBay and took the covers off and sure enuff my tantalum cap is blown and the whole top is gone but mine is blue instead of yellowish like urs but I don’t know the value of it since it’s blew apart could u give me a idea of what to replace it with ? Does it have to be tantulum and if so what value

[@mikesradiorepair]

Factory used a 2.2uF 25 Volt tantalum. It should be replaced with a 2.2uF 35 Volt tantalum capacitor. The higher voltage will prevent failure in the future and yes it should be a tantalum.

[@Hydrostream1972]

can you do a review on a uniden PC78LTD radio.the 50th one with the black faceplate...thanks mike from minnesota

[@mikesradiorepair]

+minnesota kid Not much to review, it's the same as a Cobra 29LTD. Same chassis has been around since the late 70's. Just cheaper build quality as time went on.

[@lesjones5684]

You are to picky 😂😂😂

[@lesjones5684]

Mine is a virgin 😂

[@edwinroldan739]

Hi I have two cobra 138xlr radios would like to have them checked. Email me

[@josephriffle124]

Thank you for responding so quickly. This an eBay radio. When it first came to the bench I looked it over for mods and removed the channel mod from the NB switch. Upon injecting the signal by the book, I was able to bring the rx sensitivity up quite a bit. Been all through the AGC circuit and tracking the voltages, seem to be fine. It haunts me that if one of the IF cans are bad, that I'll never be able to find a replacement. I wouldn't be opposed to replacing all of them if I could find a "kit". I've replaced the electrolytics throughout the receiver section that "may" cause any problems with no luck. Am I right in thinking that if one of the IF cans was bad, that it won't tune? All of the tuning of the cans, I was able to find the "peak" or "sweet-spot" of each. Cobra recommends TR5 upgrade per #1210a bulletin,... waiting on part. Cans available? BTW this radio is super on TX on both AM and SSB